Which Port On Master Cylinder is For Front, Rear Brakes?

Which Port On Master Cylinder is For Front Brakes

The master cylinder in your vehicle is responsible for controlling the brakes and the brake pressure. Ideally, you will find two ports connected with lines.

Which Port On Master Cylinder is For Front Brakes?

Traditionally, the rear port connects to the front brakes, while the front port connects to the rear brakes.

If you accidentally hook up your brakes in the wrong order or connect the wrong port to the wrong brakes, you will find that the braking is unstable. Many people often complain about locking the rear brakes if the connection ports are swopped around.

How To Identify The Master Cylinder?

Knowing how to find the master cylinder is an important part of working with it. Many inexperienced mechanics might not understand how it works or where to find it. The master cylinder can vary depending on the brakes. For manual brakes, it is found in one place. However, power-assisted brakes have it in a different spot but are still close to the brakes.

  • Manual Brakes: If you have manual brakes, the master cylinder is located close to the firewall. It will be directly connected to the brake pedal behind the enclosed part of the vehicle. This means you can see the master cylinder from inside the car.
  • Power-Assisted Brakes: With the power-assisted brakes, you have a brake booster connected to the master cylinder. Once again, both components are connected to the firewall of the engine compartment. The brake booster adds additional power to the braking system.

You should consider finding out where the master cylinder is located before taking apart the vehicle. You could be saving yourself plenty of time on useless motions and additional work.

What Are The Two Ports On The Master Cylinder?

The master cylinder might seem complicated, but when you take apart the component, you will notice two distinct ports. These ports have their responsibility in assisting the braking motion of your vehicle. These two ports are called the by-pass port and the compensating port if we break it down to Lehman’s terms:

  • By-Pass Port: Fluid movement inside the master cylinder is an important part of the vehicle. If the fluid does not move correctly, you could be dealing with failed brakes. The main purpose of the by-pass port is to supply fluid to the cylinder bore if the brakes are not being applied. It ensures everything is lubricated and ready to work when needed.
  • Compensating Port: The compensating port is the one that works the most. The main goal of this port is to compensate for the expansion and contraction of the fluid in the cylinder. It also deals with any temperature changes to keep the brakes from overheating. However, another important function is to help the master cylinder return to the starting position when brakes are not applied.

Both these ports serve an important role to keep the car going. If any of them get clogged or have issues, you could deal with overheating brakes and even damage to certain brake-related components.

How Does The Master Cylinder Work?

Knowing how the master cylinder works will give you insight when doing maintenance or fixing broken components. If you are unfamiliar with the inner workings of the master cylinder, I have broken down what happens on the inside of the master cylinder when pushing down on the brake pedal:

  1. Pushrod will drive the primary piston and compress the brake fluid inside the circuit
  2. Hydraulic pressure builds up from the up while the piston moves, which builds up pressure.
  3.  The pressure spreads through the cylinder and into the brake lines
  4. A secondary piston will compress the brake fluid in its own circuit
  5. The movement of the brake fluid through the lines will reach the braking mechanism
  6. The brakes will jump into action and stop the vehicle

While this seems like a complicated process, all of these motions happen in a fraction of a second and that is why maintenance on your brakes and the master cylinder is so important. Once you release the brake pedal, the springs that were engaged will release each of the two pistons. These pistons should then return to a normal operating position.

What Is A Tandem Master Cylinder?

You might occasionally find a tandem master cylinder in certain vehicles. The tandem master cylinder is two master cylinders that are combined into one housing case. With such a design, it enables the cylinder to control two hydraulic circuits.

Since the different ports are responsible for different wheels, the tandem option is much less complicated. You can have each wheel controlled on its own with the front and rear designs. Additionally, you can also have them diagonally connected.

What If I Reverse The Connection To The Master Cylinder?

While you definitely will still have brakes when you mix up the brake lines to the wrong ports, it could cause some issues. The pressure of the fluid inside the master cylinder is metered differently for each of the brake lines. In essence, you will find that your vehicle often puts more strain on the front brakes when braking than on the rear, to prevent the car from sliding.

If you accidentally mix up the brake lines to the wrong cylinders, you won’t notice it when driving around town or cruising. However, when slamming on the brakes or pressing the brake pedal harder than you always do, you could notice locking. The rear brakes could occasionally lock up, which might be dangerous, especially in the wet.


The master cylinder and brake ports are important components of your vehicle. Once you better understand the setup, you should be good to do your maintenance. It is easy to make a small mistake, but let us know in the comment section how you fix your master cylinder.

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